1. Field of the Invention
This invention relates to an intake system for an internal combustion engine, and more particularly to an intake system for a V-type internal combustion engine having a surge tank.
2. Description of the Prior Art
In the intake system for a V-type engine disclosed in Japanese Unexamined Patent Publication No. 60(1985)-156926, three surge tanks are respectively provided above the respective cylinder banks and above the space between the cylinder banks and communicate with the atmosphere by way of an intake air introducing passage the downstream end portion of which is trifurcated into three branches each connected to one end of one of the surge tanks. The surge tank above each of the cylinder banks communicates with the respective cylinders in the other cylinder bank through a low engine speed intake passages which are relatively long. The surge tank above the space between the cylinder banks communicate with the cylinders in the respective cylinder banks through a high engine speed intake passages which are relatively short and are provided with control valves. In a low engine speed range, the control valves are closed, and intake air introduced into the surge tanks above the respective cylinder banks flows into the cylinders through the low engine speed intake passages. In the low engine speed range, inertia effect of intake air corresponding to the equivalent length of each of the low engine speed intake passages is obtained. In a high engine speed range, the control valves are opened, and intake air is partly introduced into the cylinders through the surge tank above the space between the cylinder banks and the high engine speed intake passages, and is partly introduced into the cylinders through the surge tanks above the cylinder banks and the low engine speed intake passages. In the high engine speed range, inertia effect of intake air corresponding to the equivalent length of each of the high engine speed intake passages is obtained.
Though the larger the volume of the surge tank is, the better in order to suppress the intake air interference, the overall size of the engine becomes too large when the surge tank is simply large in size.